The present invention relates to disinfectants and, in particular, it relates to hydrogen peroxide solutions with improved disinfectant and antimicrobial properties.
A wide range of disinfectants is known, as discussed for example in Disinfection, Sterilization, and Preservation, edited and partially written by Professor Seymour S. Block, Fourth Edition, published 1991 by Lea and Febiger, Pennsylvania. Certain peroxygen compounds, chlorine compounds, phenolics, quaternary ammonium compounds and surface active agents are known for their germicidal properties. The rate of disinfection is relatively slow in many cases, and some compounds emit volatile organic compounds or leave a persistent residue in the environment.
Hydrogen peroxide is finding favour in many applications because its breakdown products, water and oxygen, are innocuous, and it tends to have broad spectrum antimicrobial activity. Broad spectrum activity is important in situations where harmful organisms are present but their identity is not known.
As hydrogen peroxide tends to be unstable and decomposes over time, steps must be taken to stabilize the hydrogen peroxide solutions for storage purposes. Various ways have been proposed to improve the stability of hydrogen peroxide compositions. For example, sodium stannate, sodium nitrate, and diethylene triamine penta(methylenephosphonic acid) have been reported as being useful as stabilizers, as disclosed in U.S. Pat. No. 5,523,012 to Winterton et al., which issued Jun. 4, 1996.
A major drawback of most disinfectants used heretofore has been the length of time needed to reduce the bacterial count after the disinfectant has been applied to a bacterially contaminated material. For example, it may take 30 minutes or more after application of the disinfectant to disinfect a treated surface. In many circumstances this rate of disinfection is far from satisfactory.
Combinations of hydrogen peroxide with various surfactants are known. For example, Winterton et al. discloses, in U.S. Pat. No. 5,523,012, a buffered disinfecting solution for contact lenses, which has from about 0.1% to about 1.0% of an ocularly compatible surfactant. Winterton discloses that, in one experiment, addition of about 0.4% anionic sulfosuccinate surfactant improved the killing time for aspergillus fumigatus to 6.9 minutes, compared to 9.4 minutes for a solution containing 0.1% nonionic surfactants. However, even 6.9 minutes is far too long for many applications.
The present invention is directed to improving the efficacy of hydrogen peroxide based solutions.
Accordingly, the invention provides an aqueous solution having a pH of from about 0.5 to about 6 and comprising i) hydrogen peroxide in a concentration of from about 0.01 to about 20 wt./wt. % of the solution, ii) at least one phosphorus-based acid in a concentration range of from about 0.05 to about 8 wt./wt. % of the solution, and iii) at least one anionic surfactant selected from the group consisting of C8 to C16 alkyl aryl sulfonic acids and alkali metal, ammonium, calcium and magnesium salts thereof, sulfonated C12 to C22 carboxylic acids and alkali metal, ammonium, calcium and magnesium salts thereof, C6 to C22 alkyl diphenyl oxide sulfonic acids and alkali metal, ammonium, calcium and magnesium salts thereof, naphthalene sulfonic acids and alkali metal, ammonium, calcium and magnesium salts thereof, C8 to C22 alkyl sulfonic acids and alkali metal, ammonium, calcium and magnesium salts thereof, alkali metal, ammonium, calcium and magnesium C8 to C18 alkyl sulfates, alkyl or alkenyl esters or diesters of sulfosuccinic acid in which the alkyl or alkenyl groups independently contain from six to eighteen carbon atoms and alkali metal, ammonium, calcium and magnesium salts thereof, and mixtures thereof, in a concentration range of from about 0.02 to about 5 wt./wt. % of the solution.
The phosphorus-based acid may be selected from the group consisting of the derivatives of phosphorous oxides in which the phosphorous atom is in the +5 oxidation state, phosphonic acids having 1 to 5 phosphonic acid groups and salts thereof, and mixture thereof. Preferably, the phosphorus-based acid is selected from the group consisting of phosphoric acid, 1-hydroxyethylidene-1,1,-diphosphonic acid, and mixtures thereof.
The solution may contain an additional component selected from the group consisting of emulsifiers, hydrotropes, detergents and mixtures thereof in a concentration of up to about 3 wt./wt. % of the solution, and preferably in a concentration of from about 0.04 to about 3 wt./wt. % of the solution. The emulsifiers and detergents may be polyoxyethylene surfactants. The hydrotrope may be selected from the group consisting of alkylated sulfonated diphenyl oxides, alkylated sulfonated diphenyl oxide salts, and mixtures thereof, and preferably is a C6 alkylated sulfonated diphenyl oxide disodium salt.
The anionic surfactant is preferably dodecyl benzene sulfonic acid or an alkali metal salt or ammonium salt thereof.
Preferably, the hydrogen peroxide concentration may be from about 0.05 to about 8 and, more preferably from about 0.5 to about 8, wt./wt. % of the solution.
Also preferably, the phosphorus-based acid may be present in a concentration of from about 0.2 to about 8 wt./wt. % of the solution.
The anionic surfactant is preferably present in a concentration of from about 0.08 to about 5 wt./wt. % of the solution.
Preferably, the pH of the solution is from about 0.7 to about 3.5.
The solution may further contain a corrosion inhibitor in a concentration of from about 0.05 to about 10 wt./wt % of the solution. Also, the solution may contain a monocarboxylic acid, a polycarboxylic acid, or mixtures thereof, in a concentration of from about 0.05 to about 4 wt./wt. % of the solution. The solution may also contain an alcohol comprising one to six carbon atoms in a concentration of from about 0.1 to about 10 wt./wt. % of the solution.
In accordance with another aspect of the invention, the present solution may be made in concentrated form for dilution by the end user with water.
In accordance with a further aspect, the invention provides a powdered formulation which can be diluted with water to produce the present aqueous solution.
In the past few years, efforts have been concentrated on developing chemicals that will be highly effective against microorganisms when highly diluted, will be low in toxicity to humans and other animals, and will not injure the environment. Of all the known disinfectants and antimicrobials, hydrogen peroxide appears to have exceptional potential, especially in terms of toxicity and injury to the environment because the decomposition products are benign. For example, at concentrations of 1-3 wt./wt. % aqueous solution, hydrogen peroxide is considered non-corrosive and non-irritating; at concentrations of 3-7 wt./wt. % aqueous solution, hydrogen peroxide is considered non-corrosive but an eye irritant; and at concentrations of above about 8 wt./wt. % aqueous solution, hydrogen peroxide is considered corrosive, more so at higher concentrations, and also a strong oxidizing agent.
The higher concentration levels of hydrogen peroxide solutions required to provide fast, effective action are not practical or economically viable, may be subject to hazardous goods regulations and require special precautions for handling and use. Heretofore, one of the major drawbacks of hydrogen peroxide, in low concentrations, is that its antimicrobial action is too slow. A second major drawback is that it has not been considered possible to stabilize the peroxide sufficiently to make the solution commercially acceptable. For example, prior references indicate that a 0.1 wt./wt. % aqueous solution of hydrogen peroxide requires 60 minutes to disinfect surfaces contaminated with staphylococcus aureus, whereas a 25.8 wt./wt. % aqueous solution of hydrogen peroxide requires only 20 seconds to disinfect surfaces contaminated with staphylococcus aureus. The latter solution is clearly unacceptable for commercial use, both from a safety standpoint and an economic standpoint.
It has now been found that the addition of phosphorus-based acids and certain anionic surfactants greatly, and surprisingly, enhances the bactericidal and/or virucidal activity of aqueous hydrogen peroxide solutions. The phosphorus-based acids are inorganic acids or organic acids. Especially preferred are phosphorus-based acids selected from the group consisting of the derivatives of phosphorous oxides in which the phosphorous atom is in the +5 oxidation state and phosphonic acids having 1 to 5 phosphonic acid groups and salts thereof.
More preferably, the phosphorous based acids are phosphoric acid (H3PO4), sodium tripolyphosphate, and phosphonic acids consisting of 1-hydroxyethylidene-1,1,-diphosphonic acid, amino tri(methylene phosphonic acid), diethylenetriaminepenta-(methylene phosphonic acid), 2-hydroxyethylimino bis(methylene phosphonic acid), ethylene diamine tetra(methylene phosphonic acid). Each may be used alone but mixtures of phosphoric acid and at least one of the phosphonic acids are preferred. Some of these phosphonic acids are available from Albright and Wilson under the trade mark BRIQUEST and some from Solutia Inc. under the trade mark DEQUEST.
The preferred phosphorous based acids are also known for their sequestering properties and serve, advantageously, to stabilize the solution against hydrogen peroxide degradation. These stabilizing properties are particularly important in respect of solutions containing higher concentrations of hydrogen peroxide which tend to break down quickly. Thus, solutions of the present invention also have a long shelf life, e.g. up to a year or more.
Solutions according to the invention have phosphorus-based acids in a concentration of from about 0.05 to about 8.0 wt./wt. % of the solution, preferably from about 0.20 to about 8 wt./wt. %, and more preferably from about 0.20 to about 6 wt./wt. %. The solution may be ready-to-use or concentrated so as to require dilution by the end user. The lower concentrations are used in ready-to-use formulations, while higher concentrations are used in commercial liquid concentrates.
The anionic surfactant enhances the bactericidal activity of the solution and is selected from the group consisting of C8 to C16 alkyl aryl sulfonic acids and alkali metal, ammonium, calcium and magnesium salts thereof, sulfonated C12 to C22 carboxylic acids and alkali metal, ammonium, calcium and magnesium salts thereof, C6 to C22 alkyl diphenyl oxide sulfonic acids and alkali metal, ammonium, calcium and magnesium salts thereof, naphthalene sulfonic acids and alkali metal, ammonium, calcium and magnesium salts thereof, C8 to C22 alkyl sulfonic acids and alkali metal, ammonium, calcium and magnesium salts thereof, alkali metal, ammonium, calcium and magnesium C8 to C18 alkyl sulfates, alkyl or alkenyl esters or diesters of sulfosuccinic acid in which the alkyl or alkenyl groups independently contain from six to eighteen carbon atoms and alkali metal, ammonium, calcium and magnesium salts thereof, and mixtures thereof.
Of the listed anionic surfactants, the C8 to C16 alkyl aryl sulfonic acids and their aforesaid salts are preferred as they are widely available and relatively inexpensive. They are also biodegradable. Preferred alkyl aryl sulfonic acids and their salts are dodecyl benzene sulfonic acid, and tridecyl benzene sulfonic acid and their salts, e.g. sodium, potassium, ammonium salts.
Of the sulfonated C12 to C22 carboxylic acids and their aforesaid salts, sulfonated 9-octadecanoic acid, disodium 2-sulfo C12-C18 fatty acid salts and sodium methyl-2-sulfo C12-C16 esters are preferred.
A preferred salt of naphthalene sulfonic acid is sodium alkyl naphthalene sulfonate.
Preferred salts of C8 to C22 alkyl sulfonic acids are sodium octyl (C8) sulfonate, sodium C14-C17 sec-alkyl sulfonate, and the sodium salts of 1-octane sulfonic acid, 1-decane sulfonic acid, and tridecane sulfonic acid.
Of the aforesaid C8 to C18 alkyl sulfates, sodium lauryl sulfate and sodium octyl sulfate are preferred.
Of the alkyl or alkenyl esters or diesters of sulfosuccinic acid in which the alkyl or alkenyl groups independently contain from six to eighteen carbon atoms and alkali metal, ammonium, calcium and magnesium salts thereof, disodium laureth sulfosuccinate and sodium dioctyl sulfosuccinate are preferred.
The C6 to C22 alkyl diphenyl oxide sulfonic acids and alkali metal, ammonium, calcium and magnesium salts thereof are required if the solution is to be an effective virucide. In such formulations, C6 and C10 alkylated sulfonated diphenyl oxide disodium salt are the most preferred. However, also preferred are other alkylated sulfonated diphenyl oxide disodium salts, including dodecyl diphenyl oxide disulfonic acid and disodium 4-dodecylated diphenyloxide sulfonate.
The solution may contain each anionic surfactant alone or in combination with each other. A preferred mixture of anionic surfactants is a combination of dodecyl benzene sulfonic acid and C6 alkylated sulfonated diphenyl oxide disodium salt. A solution according to the invention having these anionic surfactants will serve both as a bactericide and as a virucide.
The anionic surfactant is present in a concentration of from about 0.02 and 5 wt./wt. % and preferably from about 0.08 to about 3.6 wt./wt. %. Again, the higher amounts apply to the concentrate forms of the solution while the lower amounts apply to the ready-to-use forms.
Concentrated forms of the present solution may contain up to about 20 wt./wt. % hydrogen peroxide and preferably up to about 8 wt./wt. %. Ready-to-use preparations may contain from about 0.01 to about 1.0 wt./wt. %. As will be illustrated by the examples which follow, solutions of about 0.5 wt./wt. % are effective in substantially reducing bacterial and/or viral activity.
Solutions having about from about 0.01 to about 1.0 wt./wt %, especially about 0.5 wt./wt. % hydrogen peroxide are suitable for use as household and commercial disinfectants, bactericides and/or virucides, sanitizers and cleaners. Solutions having about 3 to about 4 wt./wt. % are suitable for use as multi-purpose cleaners and bleach alternatives in healthcare facilities, households and commercial facilities. Solutions having about 6 to about 8 wt./wt. % hydrogen peroxide are suitable for use as a sporicides, fungicides, virucides and/or bactericides, broad spectrum sanitizers, general purpose cleaners, and bleach alternatives, particularly in institutional, healthcare and food applications.
Other surfactants, in the form of detergents, emulsifiers or hydrotropes, may be present in the solutions. For example, certain emulsifiers, detergents, and hydrotropes are beneficial for cleaning surfaces with organic matter or grease and for providing stability to the solution. Typically, the emulsifiers, detergents and hydrotropes are present in a total concentration of about 10 to about 30 parts per hundred parts of hydrogen peroxide or up to about 3 wt./wt. % of the solution. Preferably, they are present in a concentration of from about 0.04 to about 2.0 wt./wt. %, and more preferably from about 0.1 to about 2.0 wt./wt. % of the solution.
Preferred emulsifiers and detergents are non-ionic alkylated alkoxylate surfactants, preferably polyoxyethylene surfactants. Preferred polyoxyethylene surfactants are alkyl polyoxyethylene surfactants and alkyl aryl polyoxyethylene surfactants. A preferred alkyl polyoxyethylene surfactant which is a detergent is C6-C10 alkyl, 3.5 moles of ethylene oxide (EO) alcohol ethoxylate (AE) sold in association with the trade-mark Alfonic L610-3.5. Also, preferred alkyl aryl polyoxyethylene surfactants which are emulsifiers are C8 to C16 alkylphenol alkoxylates. These include octyl phenol ethoxylate which is sold in association with the trade mark TRITON X405.
Preferred hydrotropes are alkylated sulfonated diphenyl oxides and alkylated sulfonated diphenyl oxide salts, e.g. C6 alkylated sulfonated diphenyl oxide disodium salt (which is also useful as an anionic surfactant, as noted above).
The pH of the solutions is from about 0.5 to about 6, and more preferably from about 0.7 to about 3.5. Preferred ready-to-use solutions have a pH from about 1.5 to about 3.5. Preferred concentrate versions of the inventive solution have pH values ranging from about 0.7 to about 2. To achieve the preferred pH values, buffering agents may be added to the solution. These buffering agents include phosphoric acid, and sodium or potassium hydroxide, the latter being otherwise known as caustic potash.
Additional additives may be added to further enhance performance. These include a short-chain alcohol, e.g. a C1-C6 alcohol, especially methanol, ethanol, iso-propanol, n-butanol and n-pentanol. Preferably, the short chain alcohol is present in a concentration of from about 0.1 to about 10 wt./wt. % of the solution. Addition of the alcohol is believed to provide improved germicidal activity and additional cleaning ability for organic contaminants.
A corrosion inhibitor may be added for the purpose of improving compatibility of the solution with non-ferrous metals. Examples include a benzotriazole, a hydrobenzotriazole, a carboxybenzotriazole, sodium nitrite, sodium molybdate, sodium gluconate and sodium benzoate and combinations thereof. When included, the preferred concentration is from about 0.05 to about 10 wt./wt. %, more preferably from about 0.05 to about 1.5 wt./wt. %.
Naturally occurring carboxylic acids such as monocarboxylic acids, polycarboxylic acids, and mixtures thereof may be added. These ingredients have known pH buffering, stabilizing and cleaning properties. Preferred monocarboxylic acids are glycolic acid and acetic acid. A preferred polycarboxylic acid is citric acid. When included in the solution, they are present in a concentration of from about 0.05 to about 4.0 wt./wt. % of the solution.
To enhance the marketable qualities of the product, additives such as colouring agents or dyes and scents or fragrances may be added.
Because hydrogen peroxide has a broad spectrum of activity, it is useful in many different applications. In the healthcare field, the solution may be used in hospitals, clinics, laboratories, dental offices, home care and chronic care facilities. It may also be used in food and beverage processing and preparation, animal husbandry, the hospitality industry and for general sanitation, e.g. janitorial services.
A preferred method for preparing the solutions of the present invention comprises adding the phosphorus-based acid(s) and the anionic surfactant(s) and optionally the emulsifiers, detergents and/or hydrotropes to distilled or otherwise purified water prior to the addition of hydrogen peroxide. If there are any other ingredients, e.g. alcohols, scents, colouring agents, dyes, corrosion inhibitors, naturally occurring carboxylic acids, these are preferably added before the hydrogen peroxide. To achieve the desired pH, buffering agents may be added following the addition of the hydrogen peroxide.
It will be clear to the person skilled in the art how to manufacture a powdered concentrate which can be dissolved in water by the end user to produce an aqueous solution according to the invention. Similarly, it will also be clear to the skilled person how to make an even more concentrated disinfecting solution than the solution described herein. Therefore, the present invention is directed also to concentrated versions of the present inventive solution and a powdered concentrate which may be dissolved in water to form the present liquid solution. In powdered form, the hydrogen peroxide is present as sodium percarbonate or sodium perborate. The phosphorus based acid and anionic surfactants are either in salt form or in acid form, as will be understood by the person skilled in the art.
The invention may also be better understood by reference to the following examples: